Anyone has some suggestions for working with black fondant.
What should I roll it out in, the cornstarch makes white marks
all over???

I use a clean white towel and just wipe it off. Comes off great. Just worked with some today.

I roll my fondant using shortening instead of cornstarch or powdered sugar. I find that it works much much better and doesn't get too dry!

Like prterell - but I spray my surface with pam.... Pam or shortening also add a slight sheen to the fondant.

I've used cocoa powder before instead of the cornstarch

wipe it down with shortening after you are done; cures all ills

Or skip the cornstarch/powdered sugar and just roll on (or between) large pieces of acetate, silicone, or even upholstery plastic from JoAnne fabric.